1. Field of the Invention
This invention relates to electronic components. More particularly, it relates to electric double layer capacitors, suitable for electro-storage devices, such as back-up power source for real time clocks.
2. Description of the Prior Art
Heretofore, there have been known electrochemical components such as aluminum electrolytic capacitors, electric double layer capacitors and electrochromic display devices, containing an electrolyte solution comprising a quaternary salt of an amidine compound (Shiono et al, U.S. Pat. No. 5,870,275).
It is an object of the present invention to provide an electric double layer capacitor having an improved stability of electrochemical properties.
It is another object of this invention to provide an electric double layer capacitor having a suppressed self-discharge.
It is still another object of the invention to provide an electric double layer capacitor having increased build-up capacity of electric charge.
It is yet another object of the invention to provide an electrolytic solution, having improved electrochemical stability, suitable for use in electronic components.
It is further object of the invention to provide a method for suppressing self-discharge in an electronic component.
Briefly, these and other objects of this invention as hereinafter will become more readily apparent have been attained broadly by an electric double layer capacitor, containing an electrolytic solution (A) comprising an electrolyte, a solvent and a polymer (I) dissolved therein.
The electrolytic solution (A) has an electrolyte ion diffusion resistance (R) higher than an electrolyte ion diffusion resistance (R0) of an electrolytic solution (A0) composed of the electrolyte and the solvent without the polymer (I). The electrolyte ion diffusion resistances (R) and (R0) are determined in accordance with alternating impedance method, at 25  C. under conditions of bias of 2.5 V and alternating voltage of 5 mV varying alternating frequency from 1 mHz to 20 kHz.
The polymer (I) has a weight-average molecular weight of at least about 2,000 or a polymerization degree of at least 4.
In another aspect, this invention embraces an electrolytic solution (A1) comprising an electrolyte, a solvent and a polymer (I) dissolved therein.
The electrolytic solution (A1) having an electrolyte ion diffusion resistance (R1) higher than an electrolyte ion diffusion resistance (R0) of an electrolytic solution (A0) composed of the electrolyte and the solvent without said polymer (I). R1 and R0 are determined, in the same manner as above, with use of an electric double layer capacitor containing an electrolytic solution between activated carbon electrodes faced each other separated with a separator.
In still another aspect of the invention, is provided a method for suppressing self-discharge in an electronic component containing an electrolytic solution. This method comprises incorporating in the electrolytic solution a polymer (I) to be dissolved therein. The polymer (I) provides an electrolytic solution (A2) composed of 2% by weight of said polymer (I), 10% by weight of tetraethylammonium tetrafluoroborate and 88% by weight of propylene carbonate and having an electrolyte ion diffusion resistance (R2) higher than an electrolyte ion diffusion resistance (R0) of an electrolytic solution (A0) composed of the electrolyte and the solvent without said polymer (I). R2 and R0 are determined, in the same manner as above using the same capacitor as above.